Inside Extreme Scale Tech|Wednesday, November 26, 2014
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United Slices through the Skies with Split-Scimitar Winglet 

As the first airline to implement the eye-catching “split scimitar” winglets, United Airlines is turning heads this week as the testing for the new design begins.

Named for a curved medieval saber, the split scimitar is a retrofit for traditional winglets that extend up at a plane’s wing tips. And while the design might catch your attention, the ultimate goal is to increase lift while cutting back on drag, which is plain terms leads to better fuel economy while the plane is in the air.

Although winglets are far from new, this particular design is unique in that rather than having a single swept-back winglet extending up from the wing, the split-scimitar design features two winglets, with the longer of the two pointed up and the shorter pointed downward. The result, United says, is a performance boost by up to 2 percent when compared to the current winglet used in the airline’s fleet.

Once the design is rolled out to its Boeing 737-900 and 737-900 models early next year, United estimates that it will save $200 million annually.

On the outside, changes such as these have done little to alter the profile of the iconic Boeing 707 that defined the age more than 60 years ago, but computer-aided engineering (CAE) has helped to make countless tweaks that results in more efficient flying.

And as fuel prices climb, jet fuel now accounts for a whopping third of airline expenses, making seemingly small changes far more important than one might initially expect.

In 2000 jet fuel cost a mere 85 cents per gallon when compared to today’s price that hovers upward of $3 per gallon. So when engineers find a winglet design that improve fuel performance by as much as 5 percent in a single flight, it means savings in the range of millions per year for just one plane.

To help mitigate these costs, airlines have turned to everything from taxiing with just one of two engines running to using lighter paper for their in-flight magazines, but the real difference comes from CAE-backed advances in engine and aircraft design.

The two current planes that are championing this are the Boeing 787 Dreamliner and the Airbus A350, both of which are expected to drop fuel consumption by about 20 percent thanks to advanced materials like carbon composites.

Although neither plane features winglets, they both use a raked design that offers a similar effect on fuel economy. In addition, Airbus is working on its own version of the split-scimitar design that it calls “sharklets.”

Airbus plans to use the design for its A320 series, but an accusation of patent infringement from split-scimitar designer Aviation Partners is bringing the case for international arbitration in London.

For airlines that need to provide a boost for their existing planes, innovations such as the winglets are key since they can be retrofitted to planes that are already in commission.

“There are still some basic physics that we use to minimize the drag on the airplane, and that hasn’t changed much over the years,” says Robert D. Gregg, III, chief aerodynamicist at Boeing Commercial Airplanes.

Nonetheless, designs vary between plane models, with wingtips looking like anything from a big “O” to a slanted arrow. But the underlying principle is that by extending the length of the wing, engineers can boost fuel efficiency.

Unfortunately, while it’s simple to understand this, the rules established by airports have put a cap on wind length to ensure that a given number of planes will be able to fit around a terminal, which is why engineers are looking to curve their wing tips up for that extra bit of lift.

The new scimitar design, the result of a joint venture between Boeing and Aviation Partners, is expected to improve upon current winglets by between 30 and 40 percent. If this proves true, United would save 45,000 gallons of jet fuel and cut 475 tons of carbon emissions every year.

Although the winglets can cost up to $2 million for larger aircraft, winglet adoption has historically led to a quick payoff, which United is banking on.

“In an environment where the price of fuel is high, you can pay off a set of winglets in under two years,” says Joel Booth, managing director of operations planning and fuel efficiency for United.

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